1. Field of the Invention
This invention relates to single lens reflex cameras and more particularly to a single lens reflex camera which is equipped with a view finder mirror having a portion for allowing light passage therethrough, a support member for the mirror having a portion for allowing light passage therethrough and a light shielding member positioned on the opposite side of the support member to the mirror to open and close the light passage portion of the support member.
2. Description of the Prior Art
The aforesaid type single lens reflex camera has already been disclosed in Japanese patent application No. Sho 54-89113 (Japanese Laid-Open Patent Publication No. Sho 56-12626) assigned to the same assignor.
That is, the single lens reflex camera described in the specification of this patent application includes a main or view finder mirror having a light-permeating property in at least a portion thereof as a light passage allowing portion and is supported by a movable first supporting member having an opening for light passage as a light passage allowing portion, an auxiliary mirror supported by a movable second supporting member for reflecting the light passed through the opening of the first supporting member incident upon a photosensitive element when the main mirror is positioned in the optical path of a picture taking optical system by the first supporting member. In other words, when in a viewing position, or in a non-shooting position, a light shielding member shuts the opening of the first supporting member when shooting, or more strictly speaking, when the main mirror is restricted by the first supporting member, and the auxiliary mirror is restricted by the second supporting member, each is toward the outside of the picture taking optical path.
In prior camera art, it is generally required that their mirror boxes are light tight with respect to other light than that coming from the picture taking optical systems, for example, light entering backward through an eyepiece. This is necessary to ensure that the film is exposed only by the light from the picture taking optical system.
With respect to the single lens reflex camera described in the above referred to Japanese patent application, as far as the ideal design is concerned, the size of the light shielding member may be of a sufficiently large size relative to the opening for the light passage formed in the aforesaid first support member so that light-tightness can be secured. In actual practice, however, with regard to the light shielding member, for example, to allow for avoidance of mechanical interference with the auxiliary mirror and because, in the aforesaid viewing position, it is required that the light beam going from the auxiliary mirror to the photosensitive element be safe from any influences, a much-desired increase cannot be effected. With respect to the aforesaid light passage opening, on the other hand, if this is made smaller, the amount of light incident upon the photosensitive element is reduced. Therefore, this cannot be decreased as much as desired. Thus, the designer must, under considerable restrictions, determine the size of each of the openings and the light shielding members within very narrow ranges of numerical values.
Consideration of the tolerances for each design parameter within which the opening and light shielding members may be manufactured and later assembled economically, result in an increase in the percentage of complete mirror boxes which will be found unacceptable because of the lack of sufficient light-tightness.
With situations described above in mind, an object of the present invention is to provide an improved single lens reflex camera making it possible to reduce the possibility of the drawbacks described above.
Another object of the present invention is to provide a single lens reflex camera in which a view finder mirror having a portion for allowing light passage therethrough is supported by a movable supporting member having a portion for allowing light passage therethrough, while still permitting a novel improvement ensuring the required degree of light-tightness during photographing.
According to the present invention, a single lens reflex camera is proposed which includes a view finder mirror having a portion for allowing light passage therethrough and supported on a movable supporting means having a portion for allowing passage of light therethrough, and first and second light shielding means cooperating with each other to shut the light passage allowing portion of the supporting means so that the mirror is retracted from the picture taking optical path by the supporting means.
A further object of the present invention is to provide full assurance for the mirror box light-tightness under the above-described object and features by using a simpler structure, therefore, without involving any unduly large increases in the complexity and bulk of the mechanisms within the camera and by very low unit cost production techniques.
According to a preferred embodiment of the present invention which will be described more fully later, a form is employed whilst the aforesaid first light shielding means is movable relative to the light passage allowing portion of the supporting means as in the prior art. The aforesaid second light shielding means remains stationary relative to the light passage allowing portion of the supporting means during the mirror operation.
In this case, the aforesaid fixed or second light shielding means may be constructed in the form of, for example, a mask member. Also, in this case, for the purpose of protecting the mask member from damage due to external shocks, it is advantageous to place the mask member between the mirror and the supporting means. Furthermore, in this case, it is an advantage that the mask member is very thin, or, for example, an opaque foil-like shape. The use of the fixed or second light shielding means in the form of a mask member gives the following additional advantage. When the movable or first light shielding means is in a position away from cooperation with the fixed or second light shielding means, or in a position where the light passage allowing portion of the supporting means is not shut, some of the light rays arriving at the light passage allowing portion are reflected from the side wall of the light passage allowing portion (i.e. opening) as harmful rays of light within the normal emerging light rays can be substantially prevented from occurring by the second light shielding means.
To facilitate a further advance in completely closing off the light passage allowing portion of the supporting means, it is advantageous to construct the movable or first light shielding means to nest at least a portion thereof within the light passage allowing portion (opening) of the supporting means. Of course, in this case, the fixed or second light shielding means takes the aforesaid form of the mask member between the mirror and the supporting means. It is to be noted that the mask member may be made of an elastic material such as rubber. That is, it is also an advantage that the mask member also serves as a shock absorber for the first light shielding means.
The foregoing concrete features are all fully disclosed in the following description of preferred embodiment of the invention.
These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.